1. Field of the Invention
The present invention relates to an image forming device for forming image data on the basis of font data and image data with a memory assignation system, so called a bit map system for storing the font data and image data. The image is formed on the basis of the font data and image data.
2. Description of the Prior Art
An image forming operation is performed by adopting so called a bit map system in a graphic display device or a laser printer employing a laser optical system and electrophotographic system. In such a bit map system there is provided an image memory (bit map memory) having its capacity for suitably storing image element data (referred to as image data hereinafter) generally corresponding to the volume of one page data. The image data sent from an external device such as a host computer or word processor are once depicted in the bit map memory. In case that the image data is a character code, the image data is depicted in the bit map memory with reference to the font data stored in the font memory.
In the bit map system, although it is required to provide an expensive bit map memory with a large capacity, the bit map system has an advantage that it is possible to finely control the location, direction, shape and size of a character included in the image and also possible to depict any image information besides the character data.
In the font memory, there are previously stored font data of generally a standard style of type (penmanship) such as Ming type or Gothic type. In the case of forming an image including a character style other than the standard style such as a character created by user or brush writing style, necessary font data are loaded down from an external device so as to be stored in a font load area in the font memory.
In the conventional memory assignation system, the bit map area for use as a bit map memory storing image data is independent of the font load area for use as a font memory. In other words, there are provided a memory area with a predetermined capacity as a bit map area as mentioned above and also provided another memory area with a predetermined capacity as a font load area whose data is accessed by an address system other than the address system for accessing the image data stored in the bit map area, so that there are secured two memory areas each having a predetermined capacity for storing a predetermined amount of data in the bit map area and font load area respectively.
Therefore, the amount of the total capacity of the memory areas is increased so that a large capacity memory device is required. In other words, in many cases of image forming, there is an empty or blank area without a data stored, so that there is a problem that the efficiency of utilizing the memory area is low.
For example, in such a large capacity memory device provided with a font load area capable of storing some kinds of font data for forming an image composed of some kinds of character styles, when an image of only the standard character style is formed, since it is not necessary to store a font data sent from the external device into the font load area, the font load area is not used. On theother hand, when a small image is formed and printed onto a sheet of small size paper, since the amount of the image data is small, there occurs a blank area in the bit map area.
In order to solve the problem mentioned above, there has been considered a memory assignation system having a memory area of the same address system in common use for storing both font data and image data. That is to say, according to the volumes of the respective font and image data, the font load area and the bit map area are appropriately expanded or reduced by controlling the assigned memory area.
However, in this system, since the expanding range of the respective areas is limited in the memory area having a limited capacity, it has been difficult to store both of the font and image data in a common memory area in practice.